Molecular sieves have been well known for many years. The first known molecular sieves were crystalline aluminosilicates and were named zeolites. Both naturally occurring and synthetic zeolites now number over 150 species. In general, the crystalline zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra and are characterized by having pore openings of uniform dimensions, having a significant ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent crystal structure.
Other crystalline microporous compositions are known which are not zeolitic but which exhibit the ion-exchange and/or adsorption characteristics of the zeolites. These include: 1) a pure silica polymorph, silicalite, having a neutral framework containing neither cations nor cation sites as disclosed in the U.S. Pat. No. 4,061,724; 2) crystalline aluminophosphate compositions disclosed in U.S. Pat. No. 4,310,440; 3) silicon substituted aluminophosphates as disclosed in U.S. Pat. No. 4,440,871 and 4) titanium substituted aluminophosphates as disclosed in U.S. Pat. No. 4,500,651.
Applicants have synthesized a new series of molecular sieves composed of germanium and at least one M.sup.+m framework element, where M includes metals such as niobium, gallium and tin and m is an integer from +2 to +5. Silicon and titanium also can be framework elements. The molecular sieve is represented by the empirical formula EQU A.sub.[(4+4y(4-m))/n] (Ge.sub.1-x M.sub.y.sup.+m Ti.sub.z.sup.+4).sub.4 (Ge.sub.1-p Si.sub.p).sub.3 O.sub.16
where A is a cation such as alkali metals, alkaline metals and hydronium ions having a valence of +n, x varies from about 0.01 to about 1.0, y varies from 0 to about 1.0, x=y+z, z has a value of zero to about 1.0 and p varies from 0 to about 0.99. When z is zero, M is Nb.sup.+5, Ta.sup.+5, Sb.sup.+5, or Sn.sup.+4. These materials are characterized in that they have the crystal structure of pharmacosiderite.
Pharmacosiderite occurs in nature, has the formula EQU KFe.sub.4 As.sub.3 O.sub.12 (OH).sub.4.6-8H.sub.2 O
and has a cubic unit cell with an edge length of 7.91 .ANG.. The structure consists of a three-dimensional network of eight-ring channels bounded by both octahedra (FeO.sub.6) and tetrahedra (AsO.sub.4). There are reports in the art of other materials having the structure of pharmacosiderite. For example, U.S. Pat. No. 3,329,481 discloses a titanium silicate designated TS-26 which has the structure of pharmacosiderite. U.S. Pat. No. 3,622,268 discloses a composition having the formula EQU M.sub.x H.sub.3-x ((Al.sub.y Fe.sub.1-y).sub.4 (P.sub.q As.sub.1-q).sub.3 O.sub.16).zH.sub.2 O
and having the pharmacosiderite structure. Other references which disclose materials with the pharmacosiderite structure include: Acta Cryst., 12, 252 (1959); J. Chem. Soc. Chem. Commun., 1566 (1987); Zeolites, 10, 730-737 (1990); Chem. Mater., 4, 468-72 (1992).
None of the references discloses a metallogermaniumtitanate having a pharmacosiderite structure. There is also no hint from these references that such a composition with said structure could be synthesized.